Arthropod trace fossils from Eocene cold climate continental strata of King George Island, West Antarctica ALFRED UCHMAN, ANDRZEJ GAŹDZICKI, and BŁAŻEJ BŁAŻEJOWSKI Uchman, A., Gaździcki, A., and Błażejowski, B. 2018. Arthropod trace fossils from Eocene cold climate continental strata of King George Island, West Antarctica. Acta Palaeontologica Polonica 63 (2): 383–396. Siltstone and sandstone beds of the Mount Wawel Formation (Eocene) contain trace fossils interpreted as insect rest- ing traces and arthropod trackways, the latest determined as Glaciichnium australis isp. nov. and cf. Pterichnus isp. Glaciichnium is included in a new ichnofamily Protichnidae, which embraces invertebrate trackways composed of straight central trail(s) and lateral tracks. The same deposits contain fragments of plant stems in growth position, delicate fern-like plant twigs and leaves of Nothofagus. Their deposition took place in very shallow but flowing water, probably in a marginal part of a lake, perhaps in a delta. The presence of mudcracks proves incidental exposure of the sediment. The trace fossils were produced by arthropods, especially insects and/or isopods, between episodes of deposition and were influenced by the water flow and subtle changes in substrate consistency. This resulted in several morphological variants of the traces. Glaciichnium australis is similar to those produced by some caddisflies (Trichoptera) in shallow puddles in the Tatra Mountains of Poland. The arthropod-dominated trace fossil assemblage is similar to the Glaciichnium ichno- coenosis, which is known from some Pleistocene lacustrine varve sediments of Europe. This fits well with the beginning of climatic cooling in Antarctica during the late Eocene. This also shows the recurrence of some ichnological features on both ends of the globe in similar palaeoenvironmental conditions and supports basics of the ichnofacies concept. Key words: Arthropoda, trace fossils, taphonomy, Antarctica, King George Island, Eocene. Alfred Uchman [[email protected]], Institute of Geological Sciences, Jagiellonian University, Gronostajowa 3a, 30-387 Kraków, Poland. Andrzej Gaździcki [[email protected]] and Błażej Błażejowski [[email protected]], Institute of Paleobiol- ogy, Polish Academy of Sciences, Twarda 51/55, 00-818 Warszawa, Poland. Received 9 February 2018, accepted 19 April 2018, available online 22 May 2018. Copyright © 2018 A. Uchman et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License (for details please see http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Pleistocene varved clay beds in the Northern Hemisphere. Introduction The aim of this paper is to describe and interpret these trace The Southern Hemisphere Cenozoic glaciation began in the fossils, one of which appears to be a new ichnospecies. Its Antarctic at the end of the Eocene and led to the first ap- interpretation was aided by observations of Recent traces in pearance of ice sheets at the Eocene–Oligocene boundary, the Tatra Mountains (Central Western Carpathians, Poland). ca. 34 Ma (Birkenmajer et al. 2005; Davies et al. 2012). This Institutional abbreviations.—GSE, British Geological Sur- climatic change significantly influenced continental biota. vey, Edinburgh, UK; ZPAL, Institute of Paleo bio logy, Polish One of the most important records of the changes occurs in Academy of Sciences, Warszawa, Poland. continental clastic- volcanoclastic sediments of the Eocene Mount Wawel Formation (Point Hennequin Group) on King George Island, South Shetlands (Fig. 1), in which leaves of the Nothofagus–Podocarpaceae assemblage have been found Geological setting (Birkenmajer 1981, 2003; Birkenmajer and Zastawniak 1989; Dutra 2001, 2004; Hunt 2001; Cantrill and Poole 2012). The Eocene sedimentary facies occur in the dominantly A contribution to the known invertebrate life in sedimen- volcanogenic succession of King George Island. They have tary environments of the Mount Wawel Formation comes been recognized in the Mount Wawel Formation (Point from arthropod trace fossils preserved in several morpholog- Hennequin Group) of Admiralty Bay (Figs. 1, 2), which is ical variants, which have been found in the “Dragon Glacier composed of volcaniclastic yellow, green, and grey tuffa- plant fossil beds”. They are similar to some trace fossils from ceous sandstone and tuff beds, which show mud cracks and Acta Palaeontol. Pol. 63 (2): 383–396, 2018 https://doi.org/10.4202/app.00467.2018 384 ACTA PALAEONTOLOGICA POLONICA 63 (2), 2018 A 62o S a g e King George Is. s s P a k e r a D AND SL o E I 62 15'S ANTARCTICA RG EO G G IN K Admirality BayB t a i t r S l d e f i s n r a B 020km10 59o 00'W 58o 00'W B Platza Point 10 Szafer Ridge Ridge m 15 m r G sso laci fe er m 15 ro 100 flora P 20 Tern Nunatak 1956 1956 m 2001 MARTEL INLET Krak Glacierm glacier front with date d Wanda Glacierm Smok Glacier m 300 d Holocene 20 Glacier m Recent and raised beach Warkocz marginal and median moraine (m) ragon Gl D acie 20 m r ?Late Pleistocene p 15 Mt. Wawel 288 residual moraine Point 15 m Bell Hennequin 15 Paleogene p Zygmunt m KRAKÓW Admiralty Bay Gp: Hypabyssal p plugs (p), dykes (d) intrusions p 200 ICEFALL Oligocene–Eocene Mount Wawel Fm. Point Hennequin Viéville Gracier Fm. Group Fig. 1. Map of King George Island (A) and location of the study region (B), after Birkenmajer (2002) with locality indicated (star). ripple marks (Fig. 3). A middle Eocene to late Oligocene fossil beds” was the same as the in situ occurrences of the age for the Point Hennequin Group has been proposed by “Mount Wawel plant fossil beds” from the top of the Mount Smellie et al. (1984), Birkenmajer (1989, 2001, 2003), Hunt Wawel Formation. The sandstone beds contain sedimen- (2001) and Hunt and Poole (2003). New data on the Mount tary structures with wave-formed ripple marks (Fontes and Wawel Formation points to its latest middle–late Eocene Lindner Dutra 2010; Fig. 3A), elongate plant remains associ- age (Francis et al. 2008, 2009; Nawrocki et al. 2011; Mozer ated with mud cracks (Fig. 3B), delicate fern-like plant twigs 2013; Pańczyk 2013). (Fig. 3C), and well-preserved Nothofagus leaves (Fig. 3D), The trace fossils discovered in loose, ex-situ slabs of and oblique, longitudinally striated open tubes, which are fine-grained sandstone of the Dragon Glacier plant beds probably lower plant (reed-like?) remains in growth position (informal unit) are associated with distinct facies on the (Fig. 4). They occur irregularly or in patches. Extrapolated 300-m high exposure, greatly affected by faulting ice cov- density fluctuates around 500 tubes/m2. In some bedding ering and reworking (Hunt 2001). According to Zastawniak planes, the tops of tubes are surrounded by crescentic marks et al. (1985), the origin of the ex-situ “Dragon Glacier plant indicating a consistent direction of water flow. UCHMAN ET AL.—EOCENE TRACE FOSSILS FROM ANTARCTICA 385 Mt. Wawel Dragon Glacier collection area Martel Inlet Fig. 2. Location of plant and trace fossil collection area as seen from Martel Inlet, Admiralty Bay, King George Island, Antarctica. Photograph by AG, January 2007. argument for its ichnological origin. Segmentation of the Systematic palaeoichnology axial turbinate mound corresponds to the head, thorax and Ichnofamily uncertain abdomen of an insect. The main lateral ridges are imprints of legs. The leg imprints are complete on one side and in- Resting trace complete on the other. The indistinct ridges could be cerci, Fig. 5A, D–E. however this is not clear, because they do not start from the Material.—ZPAL Tf.8/2007.8, a slab of very fine-grained termination of the interpreted abdomen. There are traces of silty sandstone, middle–late Eocene, King George Island, wings or antennae. The systematic affiliation of this insect Antarctica. structure is undetermined because of the poor state of pres- ervation; however, a beetle larva is possible. Description.—Hypichnial structure composed of an axial turbinate mound that is 21.3 mm long and associated with Ichnofamily Protichnidae nov. lateral, linear ridges. The turbinate mound is tripartite, with Type ichnogenus: Protichnites Owen, 1852; typified by Protichnites segments 3.5 m, 4.7 and 14 mm long. The longest segment septemnotatus Owen, 1852; middle–late Cambrian, eastern Canada. is the widest reaching 3.5 mm in width. Three lateral, linear Included ichnogenera: Protichnites Owen, 1852, Stiallia Smith, 1909, ridges, about 10 mm long, extended from one side of the Stiaria Smith, 1909, Siskemia Smith, 1909, Keircalia Smith, 1909, wider part of the longest segment. The ridges are slightly Mitchellichnus Smith, 1909, Paleohelcura Gilmore, 1926, Glaciich- curved, about 1 mm wide. Two of them are parallel, 3 mm nium Walter, 1985. apart. The third one, diverges at about 30° from the shorter Diagnosis.—Relatively small trackways composed of straight segments. One ridge extends from the other side of the lon- central trail(s) and lateral tracks. gest segment. It is 5 mm long, terminating in a hook, and Remarks.—Distinction between some members of the ich- inclined at about 25° to the axis of the turbinate mound. nofamily can be difficult, because their preservational vari- Additionally, two indistinct ridges are present on both sides ants can be very similar, as for instance between Stiaria, of the longest segment. One of them is slightly winding, Siskemia, and Mitchellichnus (Genise 2017) or between inverted over the ridges and passing on the other side, while these ichnogenera and Paleohelcura (Getty et al. 2017). the other runs straight outwards at an angle of 30° in respect This is mostly conditioned by subtle changes of substrate to the axis of the segment. properties, which control morphology of trackway variants Remarks.—The morphology suggests a resting trace of an (Uchman and Pervesler 2006; Davies et al.